A Volcanic View of the Habitable Zone

byPaul GilsteronFebruary 28, 2017

Our understanding of habitable zones is a work in progress, but the detection of multiple planets with potentially water-bearing surfaces around TRAPPIST-1 is heartening. Today we examine the prospect of extending the habitable zone further out from the host star than previously thought possible. The idea is found in new work by Ramses Ramirez and Lisa Kaltenegger (both at the Carl Sagan Institute at Cornell University). Volcanism is the key, allowing interactive effects that pump up greenhouse warming and sustain habitability.

Go back for a moment to the habitable zone limits that Andrew LePage looked at yesterday in his analysis of TRAPPIST-1. The classical habitable zone — allowing liquid water to exist on the surface — has an inner edge at which surface temperatures become high enough to lead to a runaway greenhouse and the rapid loss of water. The outer edge is defined by the distance beyond which CO2 can no longer produce the needed greenhouse effect to keep the surface warm.

But consider, say Ramirez and Kaltenegger, the effect of additional greenhouse gases on these worlds at the outer edge of the HZ. Here’s some context: The warming effect of hydrogen atmospheres has already been considered on young planets, allowing a primordial super-Earth to stay above freezing at the surface out to distances in the range of 10 AU. The paper explains that this greenhouse effect comes from what is known as collision-induced absorption, the result of so-called ‘self-broadening’ when H2 molecules collide.

The problem: Primordial hydrogen in the large amounts needed isn’t sustainable over geological timescales, meaning a super-Earth without a renewable hydrogen source would lose hydrogen to space. But volcanism can be the renewable source needed. The authors point out that climate studies of the early Earth and Mars both show that volcanism could have outpaced the escape of H2. Hydrogen here is not a major atmospheric constituent but is continually replenished by volcanism that offsets H2 loss.

Now we are in a situation where any atmospheric CO2 can interact with hydrogen to increase the greenhouse warming potential for the planet over long time periods. The effect could extend a habitable zone by between 30 and 60 percent. Says Ramirez:

“On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes. But if the surface is warm enough – thanks to volcanic hydrogen and atmospheric warming – you could have life on the surface, generating a slew of detectable signatures.”

Image: The eruption of the Tavurvur volcano in Papua New Guinea, part of the Rabaul Caldera on New Britain. Can similar eruptions produce the factors needed for habitability at the outer edge of the habitable zone? Credit: Taro Taylor edit by Richard Bartz – originally posted to Flickr as End Of Days, CC BY 2.0.

In terms of our own Solar System, the researchers point out that the addition of 30% H2 can extend the habitable zone to 2.4 AU, putting its outer edge in the main asteroid belt (the habitable zone around Sol is normally considered to extend to 1.67 AU, just beyond the orbit of Mars). Because we’ll be looking for atmospheric biosignatures with upcoming instruments like the James Webb Space Telescope and the European Extremely Large Telescope, we’ll want to factor this extended habitable zone into our list of search candidates.

In their paper, which appears in The Astrophysical Journal Letters, the researchers use climate models to compute the boundaries of what they are calling the ‘volcanic hydrogen habitable zone’ for concentrations of hydrogen between 1% and 50% — finding that at a hydrogen concentration at the upper end of that range, the effective stellar flux needed to support the outer edge of the habitable zone decreases by ~35% to 60%, with the corresponding orbital distances to remain habitable increasing by 30% to 60%. The effective temperatures (TEFF of the stars examined range from 2,600K to 10,000K — the stellar classes range from M dwarfs to A-type main sequence stars.

Given these prospects, how do we go about searching for life signatures on outer planets with sizeable amounts of atmospheric hydrogen? It’s a vexing question:

Certain atmospheric spectral features, including N2O and NH3, which can, but do not have to be produced biotically, could be detected in H2 -dominated atmospheres (Seager et al., 2013; Baines et al., 2014). Such volcanic-hydrogen atmospheres may also be able to evolve methane-based photosynthesis (Bains et al., 2014). Distinguishing biosignatures from abiotic sources in such atmospheres will be challenging.

Note the possibilities that must be distinguished here:

NH3 can be formed abiotically through reaction of N2 and H2 in hydrothermal vents on planets with reducing mantles (Kasting et al., 2014). N2O can be formed a number of ways including through atmospheric shock from meteoritic fall-in, lightning, UV radiation (e.g. Ramirez, 2016) and through solar flare interactions with the magnetosphere (Airapetian et al., 2016). Thus, future biosignature studies should focus on modeling biotic and abiotic sources for these gases in thin volcanic-hydrogen atmospheres.

Clearly there is plenty of work ahead, but a combined greenhouse effect from hydrogen, water and CO2 could be the key to expand stellar habitable zones and widen our observational window. As Kaltenegger puts it, “Where we thought you would only find icy wastelands, planets can be nice and warm – as long as volcanoes are in view.” And warming hydrogen, all too easily lost into space, can be renewed by the same kind of volcanic hydrogen that puffs up planetary atmospheres, making that much stronger a signal for the detection of biomarkers.

Does TRAPPIST-1, then, have the capacity for yet another planet in the habitable zone? Kaltenegger isn’t ready to go that far, saying “…uncertainties with the orbit of the outermost Trappist-1 planet ‘h’ mean that we’ll have to wait and see on that one,”

There has already been a search (with negative results) for a hydrogen dominated atmosphere for the inner 2 Trappist-1 planets using transmission spectroscopy during a mutual transit. I don’t think we will have to wait for Webb to resolve this particular issue, at least for the Trappist-1 system.

Interesting point Marshall. However, the atmospheres in our new study are not hydrogen-dominated (most contain well under 50% hydrogen) although they are hydrogen-rich. What we are proposing are mostly CO2-dominated atmospheres (near the outer edge) with some amount of hydrogen. Towards the inner edge, these atmospheres may be N2- or H2o-dominated. So these atmospheres will still be considerably denser and less “puffed up” than a pure- or hydrogen-dominated atmosphere.

If we have hydrogen and carbon bearing matetials methane can be formed which is a powerful greenhouse gas. If we look at Neptune for instance it has 1.5 % methane which would have a substantial warming effect.

Not in the sense described here. It requires volcanoes that require plate tectonics and this requires water as a lubricant . Provided via plate subduction at continental / ocean margins ( think Pacific ” Ring of Fire ” on Earth .

Venus has long lost its water so has lost its tectonics ( via a runaway greenhouse effect that independently rendered it uninhabitable ) . It’s crust is a ” stagnant lid “. This is theorised to vent internal heat build up in its outer mantle by essentially melting en masse every few hundred million years.

Where there is energy and there is a lot of it at Venus’s orbital distance
together with heavy elemental chemicals, less of them in Venus’s atmosphere, it could potentially support primitive life in Venus’s clouds.

Fascinating if such a greenhouse cocktail could be confirmed as the brew that warmed Early Mars – and Earth. So long as we’re discussing “Hydrogen Earths” several researchers have shown that planets with trapped primordial H2 atmospheres can retain liquid water even out in interstellar space. The outer limit of the Photosynthetic Habitable Zone is somewhat more restrictive, being about ~10 AU thus equivalent to ~0.01 Earth’s insolation levels. A hydrogen-rich ‘moon’ could orbit Saturn and have open water oceans with exotic plants.

An intriguing question is whether H2/O2 can exist in sufficient disequilibrium to make such outer worlds habitable by humans. If the total pressure was ~10 bar and O2 was less than 5%, but still at a breathable partial pressure, then there’s no chance of igniting the atmosphere. Hydrox is a deep-diving breathing mix which pigs have tolerated to 70 bar pressure.

Alternatively future explorers of H2/CH4 greenhouse worlds could wear simple O2 masks. Eventually we might figure out how to replace our O2 utilizing mitochondria with H2 using alternatives and do away with the masks.

Tom, thanks for your question. Yes, our HZ calculations do take into account that water stays liquid up to the critical point of water that you mentioned. On a planet with an Earth-like amount of surface water, beyond that critical point, no liquid water can exist on the surface. It instead becomes a steam atmosphere and a full-blown runaway greenhouse ensues.

The argument assumes that early rocky worlds have reducing mantles that can outgas H2. Over time this loss results in an oxidized mantle which prevents further H2 emissions.

The source of the hydrogen is from water, or some other compound? The paper argues that Mars may have released hydrogen for a billion years, while earth for only 100 m. This appears to be an empirical observation, but what is the underlying chemistry model that would support this?

Yes, where is all of this volcanic H2 supposed to have come from? Sure, it’s the most common molecule in space, but in the interiors of rocky planets that have experienced meltdowns during formation how common can it be?
Also, light gases like H2 would be the easiest for stars to strip away during a star’s very active youth.

Alex, more details are in works like Wade and Wood (2005). Essentially, Mars is too small to generate the pressures necessary to lead to mantle oxidation, favoring volcanic outgassing of hydrogen-rich products. Earth, being larger, is more likely to generate the processes that result in an oxidized mantle, leading to the eruption of more hydrogen-poor gases. Such results are predicted from lab experiments exposed to different pressures/conditions.

Dave, I’ve played around with H2S a bit in trying to warm early Mars. My experience is that it has some greenhouse effect, but it isn’t particularly strong. SO2 is the stronger sulfur species out of the two.

Could the inner two planets be as active as Io? There would seem to be a good chance that the other planets would also have an active lithosphere because of the tides caused by the nearby planets. The two inner planets could also be elongated bacuase of the interaction between the red dwarf and its high magnetic field and the planets cores causing them to stay in a molten state. What about meathane on the outer planets, could some type of lifeforms use it and what forms could it take under different tempatures and pressures?

The James Webb Space Telescope, originally intended for scanning the outer reaches of the cosmos, is now expected to break new ground exploring exoplanets.

Kevin Heng

One of the most exciting potential uses of the James Webb Space Telescope (JWST), which is scheduled to launch in 2018, is to hunt for habitable exoplanets—something that was beyond imagining at its inception. In the 1970s, no one even knew whether exoplanets existed. In the 1990s, when JWST was conceived as the successor to the Hubble and Spitzer space telescopes, the notion that the atmospheres of alien worlds could be studied seemed faintly ludicrous. Part of the early motivation was to build a telescope that would be powerful enough to detect the earliest stars and galaxies. Because the universe is expanding, which reddens light as it travels across space, this new eye on the cosmos would need to be built for the infrared spectrum. Fast forward to 2017, and the measurement of atmospheric properties of exoplanets is now fairly routine. Humanity’s most expensive telescope, originally intended for scanning the outer reaches of the cosmos, is turning out to be a decisive instrument for exploring alien worlds and—if we are lucky—will find ones that are habitable.

When JWST was conceived, studying the atmospheres of exoplanets was not on the minds of its developers. Then in 2005, photons from the atmosphere of an exoplanet were detected for the first time using the Spitzer Space Telescope. Later, astronomers learned how to record signals from these atmospheres at different colors and interpret them to identify the presence of atoms and molecules, using both space- and ground-based telescopes.

To date, water, carbon monoxide, hydrogen, magnesium, methane, sodium, and potassium have been robustly detected. Nowadays, the Hubble Space Telescope is routinely used to check whether an exoatmosphere contains water. Astronomers have also made crude temperature maps of these atmospheres. Exoatmospheric science tells us about the general climate conditions of an exoplanet, including chemistry and temperature. As technology has advanced, enabling us to probe cooler (and fainter) exoatmospheres, these discoveries have opened a potential window into studying an exoplanet’s habitability.

These recent advances are prompting changes to JWST—both in terms of tweaks to the hardware and the telescope’s operation—while it undergoes testing in preparation for its scheduled launch in October of 2018. Given the limited lifetime of JWST, which may be as short as 5.5 years, astronomers and astrophysicists are focusing on the best targets for advancing our understanding of exoplanetary atmospheres: gas and ice giants first, and a selected sample of smaller exoplanets second.

Interesting and unsurprising research results given what we know about our own system of planets and Moons.

I have often despaired at the statements of researches that claim this, that and the other based only on anecdotal evidence or assumptions.

Venus is a cauldron by Earth standards and we understand that as the young Sun increased in energy and brightness the atmosphere of the young Venus was modified. However, there are two key differences between Earth and Venus.

Earth is effectively a double planet and the gravitational tug of war clearly assists with volcanism and plate tectonics on Earth and is , in my opinion, the main reason for Earth having a powerful and global magnetic field.

This magnetic field is an important difference for our planet, will this be the case with other worlds? Well Venus lacks a decent global field that would have protected the upper atmosphere from the ravages of the early Sun’s energetic solar wind.

When calculating the alleged “habitable zones” around stars I am curious as to whether a global magnetic field, or lack of, is taken into account because clearly it is a major influence.

Lastly, without a global greenhouse effect by Water Vapour in the atmosphere Earth would actually be a frozen wasteland so as far as I see Earth validates this research.

James, you are certainly right that a magnetic field plays an important role in habitability for the Earth although some studies have suggested that magnetic fields could be *bad* for habitability in some cases.

In the case of Venus, your comments suggest that it never had one. However, Venus could have very well had a substantial early magnetic field although this is not currently known. Even with such an early magnetic field, I am not so sure that it would have been able enough to protect Venus from the ravages of an early Sun.

In my view, the potentially biggest issue with Venus is that it receives nearly twice as much solar energy as our planet does given its close proximity to the Sun. As I show in our paper (discussed here on Centauri Dreams as well : https://www.centauri-dreams.org/?p=32073), “The Habitable Zones of Pre-Main-Sequence Stars”, Venus was close enough to the young Sun that it could have been in a runaway greenhouse state for at least several million years, removing whatever water it may have had very early on. If that happened, the issue here does not have as much to do with the strength of the magnetic field, but with the resultant high surface temperatures, which could have lead to vaporization of the entire surface water inventory and total planetary desiccation.

Ramses, the proximity of Venus to the Sun does not make as large a difference as is often thought. Venus receives about 1.7x the solar flux that Earth does, however several studies have shown that with a different atmospheric composition so it was more ain to Earth the global mean temperature would be about 22°C, up from Earth’s approx 14°C.

As far as I am aware Earth’s vulcanism is predominantly if not totally driven by plate tectonics and subduction with the whole process lubricated by water (something Venus has lost along with similar vulcanism replaced by a ” stagnant lid” crust that melts every few hundred million years) . This in turn is driven by convection in the mantle .

The whole process could operate in the absence of any moon which for Earth raises significant tides in the oceans but unlike Io, is not nearly enough to do so in the crust or mantle . Io’s crust has been shown to shift hundreds of feet thanks to its substantial tidal interactions with proximal ( and massive ) Jupiter and its neighbouring moons that so heat its mantle . It’s vulcanism has a total different aetiology .

Venus is now most likely tidally locked given its slow rotation which is unlikely to produce much in the way of a Dynamo effect in its liquid outer core . Ironically extended vulcanism has been mooted as a mechanism of protecting against atmospheric erosion even in the absence of a magnetic field .

Kite et al looked at this for Super Earth’s orbiting red dwarfs the hypothesis / simulations looking at the volcanic production of secondary atmospheric gases to replenish those lost to the hostile stellar flux of early and pre main sequence red dwarfs . As long as the internal pressure in the mantle didn’t become high enough to shut down convection ( and there were enough volatiles to lubricate tectonics) as might happen with too large a terrestrial planet, they found that vulcanism on such planets could be sustained for tens of billions of years.

James, I’d like to see what study you are referring to because it contradicts not only my calculations, but all of the recent modeling on the subject.

The flux Venus receives today is over 1.9 times that received at Earth (1/(0.718^2)) ~ 1.94, a ratio of the inverse square law of their distances to the Sun.

At Earth’s distance from the Sun, newer studies (e.g. Leconte et al. 2013) obtain that a flux level only ~1.1 times that received by Earth today would trigger a runaway greenhouse. And Venus receives much more energy than this.

A magnetic field has little to do with this here. This is solely the fact that if water gets too hot, it will evaporate.

Did Venus have a long enough temperate environment to at least evolve simple lifeforms? Could they have descendants in the planet’s upper atmosphere or under the surface?

Today’s news that terrestrial microbial fossils dating back over four billion years lend some support to the idea of life evolving even in harsh conditions given enough of the right materials and climate. And we already know how life on this planet can survive in what was once considered very inhospitable conditions.

ljk, it is possible that Venus could have supported life in the past if the climate was more temperate. Some studies argue (e.g., Yang et al., 2013;2014; Way et al., 2016) that if Venus had been rotating slowly enough, a larger than normal amount of clouds could have formed on the Sun-lit side, reflecting much of the extra energy back out to space. Such conditions may have helped moderate surface temperatures on Venus even though it is closer to the Sun (maybe for a couple of billion of years or so) before it eventually lost its water to a runaway.

ljk…Another good question. This is unknown. One of my colleagues thinks that Venus’ mantle may be wet although its surface is dry. This is something that will require future missions to answer. My take is that if water is needed to lubricate plates for plate tectonics to function (that is one hypothesis), then if there is much water deep in Venus, it is somehow not being accessed to lubricate them.

Two things stand out about this. ONE: Is THIS what kept Earth warm when the Sun was only two thirds as warm as it is today(Ramses and Lisa; any thoughts. A future paper on this possibility would be fascinating)? TWO: The PRIME BENEFICIARIES of this NEW “greenhouse effect among the existing CONFIRMED planets are TRAPPIST-1g and Kepler 186f. Already IN the habitable zone but EXTREMELY COLD, BOTH of these planets COULD have much more moderate climates than previously invisioned.

Harry, we actually do not know for sure what had kept Earth warm early on (aka “the faint young sun paradox). There have been several proposed solutions to this paradox, including a similar volcanic hydrogen solution that we had used here for the habitable zone and in my 2014 early Mars paper. This volcanic hydrogen solution for early Earth had assumed a N2-H2 greenhouse combination, though, instead of CO2-H2.

To my understanding, the earth’s atmosphere used to be much thicker, which explains a number of things about our prehistoric past. A thick atmosphere distributes heat efficiently and has a larger greenhouse effect, which explains the global tropical climate of the mesozoic. The thicker air was also able to support larger terrestrial megafauna such as apatosaurus/brontosaurus and the ability of dactyls to fly.

I’m sure volcanism played a significant role in this, although there could have been other factors.

There is a NEW paper out regarding Proxima b, but with POSSIBLE IMPLICATIONS for TRAPPIST-1d on ArXiv today. ArXiv: 1702.08463. Exploring the Climate of Proxima B with the Met Office Unified Model, by Ian A. Boutle, Nathan J. Moyne, Benjamin Drummond, James Manners, Jayesh Goyal, F Hugo Lambert, David M Acreman, Paul D Earnshaw. The pertinent sentence is …”However, we find interesting differences from previous simulations, such as cooler mean temperatures for the tidally-locked case”… Rameses and Lisa. This paper is WAY OVER MY HEAD. Any comments on it would be greatly appreciated.

Harry, yes I have recently seen this paper as well. You touch on a major area of research right now that involves understanding how heat is transferred between the atmospheres and oceans on a potentially habitable tidally-locked planet. Currently, we do not understand this too well. For that matter, neither do we understand too well how clouds form/vary nor how water vapor is transferred throughout the atmosphere. All of this is necessary in order to understand atmospheric-ocean heat transport, including for tidally-locked planets. Different models make different assumptions regarding all of these aspects, and unsurprisingly, yield different answers.

I would guess that the complex and substantial interplanetary and stellar gravitational interactions would raise potent tides and currents in any putative oceans on TRAPPIST-1 planets . ( as well as Io like vulcanism ?) This apart from being impressive would certainly help transfer of heat on a tidally locked planet , even under ice ( assuming those self same tides and IR stellar flux haven’t help melted it ) and even without considering similarly heat transferring winds in any atmosphere.

Whether they have cooled is also dependent on their heat of formation and radioisotope content ( which can be age related but complicates matters unnecessarily ) . This is obviously substantially related to mass with larger terrestrial planets being hotter and potentially sustaining vulcanism for longer ( Earth after all is still going strong after 4 billion years plus ) . There is presumably an upper mass at which mantle convection driven tectonics and vulcanism can be sustained until internal pressure and resultant mantle viscosity ( and make up ) shuts down the process and a Venus style “stagnant lid” crust arises instead .

Edwin Kite, U of Chicago currently , has published extensively on this and has shown that extended vulcanism is possible in planets up to twice Earth mass at the least, though looking at the publication and author comments above this might come at the cost of a lower hydrogen output .

Whether or not plate tectonics can be sustained on rocky planets considerably larger than Earth is an ongoing area of research and there are arguments on both side of the issue. Apparently, either plate tectonics is facilitated due to higher subduction velocities or made more difficult because of increased fault strength under higher gravity. It will be some time before this question is resolved.

This will extend the life of the magnetic field and vulcanism on these planets if the core has enough Silicon and Oxygen. The crystallization zone creates enough heat when it forms Quartz to keep the core liquid for much longer. So this would still be part of the ongoing formation process by extending the cooling time because of the latent heat of crystallization.
See figure 3 In the Nature Journal letter.
The cooling rate, crystallization rate and the CMB heat flow (QCMB; with and without SiO2 crystallization) necessary to sustain the geodynamo are plotted as a function of assumed total dissipation for the time just preceding the onset of inner-core crystallization

“On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes. But if the surface is warm enough – thanks to volcanic hydrogen and atmospheric warming – you could have life on the surface, generating a slew of detectable signatures.”

Whenever air gets warm, it expands, the molecules move apart and it becomes less dense so it becomes light and rises. The result is low pressure or a partial vacuum. Cool air is more dense so it sinks. High pressure always moves towards the low pressure. The result is are winds like what happens in a sea breeze. The low pressure is over the day side of a rocky Earth exoplanet so the higher pressure air or high of the night side blows towards the low to fill in the partial vacuum so you get some kind of circulation like a Hadley cell with the cold air blowing towards day side with warm air circulating over it. It becomes more complex depending on whether it is a super Earth water world or has small oceans and a large land mass.

Quote by Ashley Baldwin: There is presumably an upper mass at which mantle convection driven tectonics and vulcanism can be sustained until internal pressure and resultant mantle viscosity ( and make up ) shuts down the process and a Venus style “stagnant lid” crust arises instead . I agree with this. I read that the water keeps the crust cool and Venus does not have that and too much pressure does not allow for that like the deep Oceans on a super Earth water world. . The convection currents in the asthenosphere or upper mantle move the lithosphere or crust. The greater temperature to the the super Earths larger size can increase the pressure according to this paper t an expert in geology. http://iopscience.iop.org/article/10.1088/2041-8205/780/1/L8

Michael Fidler, the paper “Quartz’ crystals at the Earth’s core power its magnetic field,” This paper only explains that “Crystallization changes the composition of the core by removing dissolved silicon and oxygen gradually over time.” It does not explain this statement: “We were excited because our calculations showed that crystallization of silicon dioxide crystals from the core could provide an immense new energy source for powering the Earth’s magnetic field.” This statement is unsupported so I am biased against it. I don’t see how it could work. Solid crystals in the Earths core? I don’t think they could survive such pressure. Crystals can be induced to produce an electric field through piezoelecticity if they are hit with a hammer but that won’t work in Earths core which has an extreme pressure which will crush any crystal or even diamond.

The Earths magnetic field is thought to be caused by the spinning convention currents of Earths liquid core shaped like large cylinders which rotate. This rotation causes the electrons in the iron to emit a magnetic field like the electrons in a electric current moving through a wire wrapped around a nail.

Geoffrey Hillend , (Please read the article), The crystallization zone creates enough heat when it forms Quartz to keep the core liquid for much longer. So this would still be part of the ongoing formation process by extending the cooling time because of the latent heat of crystallization.

“The researchers were surprised to find that when they examined the samples in an electron microscope, the small amounts of silicon and oxygen in the starting sample had combined together to form silicon dioxide crystals (Fig. 2)—the same composition as the mineral quartz found at the surface of the Earth.
“This result proved important for understanding the energetics and evolution of the core,” says John Hernlund of ELSI, a co-author of the study. “We were excited because our calculations showed that crystallization of silicon dioxide crystals from the core could provide an immense new energy source for powering the Earth’s magnetic field.” The additional boost it provides is plenty enough to solve Olson’s paradox.
The team has also explored the implications of these results for the formation of the Earth and conditions in the early Solar System. Crystallization changes the composition of the core by removing dissolved silicon and oxygen gradually over time. Eventually the process of crystallization will stop when then core runs out of its ancient inventory of either silicon or oxygen.”

“Our data and model also permits an alternative scenario in which crystallization proceeds at shallower depths first, with buoyant SiO2 accumulating on the top of the core and producing a denser (Si + O)-depleted liquid that would sink into the deeper core, thus helping to drive core convection.”

Venus has one big Hadley Cell due to it’s slow retrograde rotation of 243 days. Source The Scientific Exploration of Venus, Taylor. There is no Coriolis effect without a fast rotation which causes more than one Hadley cell and several high and low equatorial pressure zones on the Earth.

There is actually two Hadley cells which begin at the equator of Venus which split the atmosphere into two hemispheres. The hottest part is at the equator so the hottest rises at the equator and moves towards the poles over the cold air below it which comes from the poles.

Venus might not be a good model for exoplanets in the life belt, the area around a star where water is stable in liquid form and not ice or vapor, since most likely they do not have run away greenhouse effects there but only the ones that are too close to the star. The atmospheres of exoplanets can still be complicated, but I think we will learn a lot about them once we have accurate data from spectroscopy about their chemical composition and magnetic fields hopefully in next five to ten years.

I forgot to mention — there’s another reason why volcanism is significant. In Earth’s history, there were severe ice ages which froze most or all of the surface (see: slushball/snowball earth). The primary mechanism for warming the climate was volcanoes, which spewed greenhouse gasses that eventually accumulated and started a positive feedback loop. Without volcanic activity, it is likely that Earth would have been caught in an ‘ice trap’, unable to thaw its frozen climate due to high albedo/reflectivity of the ice.

The general idea here is that volcanism provides a safeguard against ice ages and runaway cooling, which is significant for maintaining habitability.

Michael Fidler The crystallization would have to occur in the mantle and this article implies that how ever this quote is not explained: “We were excited because our calculations showed that crystallization of silicon dioxide crystals from the core could provide an immense new energy source for powering the Earth’s magnetic field.” I don’t see how that can power Earth’s magnetic field. He’s does not explain that process. I’ve never heard of SIo2 in the core. There is sulfur and oxygen but not SI02.

I’m not expert in geology or chemistry but from what I’ve read you can’t have any crystallization in the inner or outer liquid core because of the high temperatures. Diamond crystals won’t even be able to form there. Maybe in the mantle but not in the core. The melting point of diamond is 5800 degrees. The Earths outer liquid core is 5,800 to 9,400 degrees F. Diamond will be crushed and melt as low as 87 to 120 miles in the mantle. Quartz has a much lower melting temperature at only 3115 F. Consequently, the molecular bonds of SI02 would easily break apart at those temperatures and pressure. The SI02 crystallization has to occur near the crust or top of the mantle. I don’t see a connection to the core. The heavier elements do move to the center of the planet and lighter ones or silicates always end up near the surface. This is a general principle in the geology of planetology or planetology 101. This in my opinion is not a scientifically supported paper but only an article on the web where not everything is necessarily scientific.

This is in the magazine Nature, the whole reason for the experiment was to see what formed under high pressure and temperatures near the earths core.
The crystals were not large but small like in most rocks and like metallic hydrogen, crystals can form at high temperatures because of the high pressure. We know a lot less about what is below us then what is above and I am sure that many new discoveries will be made as we study the structure of the many new types of exoplanets! As for the magnetic field, the heat created from the crystallization keeps the core liquid for a much longer period and keeps the convection currents active.

When the silicon and oxygen come out of the core, it ends up near the surface I presume through rifts, volcanic eruption, crystallization near the surface, BUT that process does not imply” an immense new energy source for Earths magnetic field,” especially since most of the Earths magnetic field comes from the larger percentage of the iron-nickel in the core.

Could these other elements add to Earth’s magnetic field? These oxygen and silicon and the others mentioned could due to pressure ionization which might make them electric conductors and give their electrons more freer emit a magnetic field since they move in circles in convection currents like the nickel iron. I am not an expert on this process and it still would be and old energy source not new. Newly discovered maybe.

“Our data and model also permits an alternative scenario in which crystallization proceeds at shallower depths first, with buoyant SiO2 accumulating on the top of the core and producing a denser (Si + O)-depleted liquid that would sink into the deeper core, thus helping to drive core convection.”
This process sounds like what is happening in the mantle: the convention currents in the mantle and temperature changes or convection might drive the fluid flow of the core but the coriolis force from the Earth’s rotation is what causes the iron to move in circles which is what causes the magnetic field.

Michael Fidler I agree with the national geographic article which says that there are iron crystals in the Earths solid core. Interesting. I never knew that, and I am not an expert in geology, but I am still biased against the idea of silicon dioxide or quartz crystals in the outer core which is liquid and the statement that crystals power the Earth’s magnetic field. Not enough information is given to explain that process. I am not saying it is wrong but just lacking in information that will allow me to see how it might work.

A giant meteor impact on Earth nearly 2 billion years ago triggered more explosive and long-lived volcanic eruptions than previously thought, a new study finds.

This finding sheds light on how meteor bombardment may have dramatically shaped the evolution of the early Earth, researchers in the new study said.

Meteor strikes have left giant craters all over Earth. For instance, the cosmic impact that scientists think ended the age of dinosaurs about 66 million years ago left behind a crater more than 110 miles (180 kilometers) wide near the town of Chicxulub (CHEEK-sheh-loob) in Mexico.

About 3.8 billion to 4 billion years ago, we know the inner solar system experienced heavy bombardment from impactors,” Kamber said. The oldest rocks on the planet coincide with the last peak of this bombardment, suggesting that “the older rocks on Earth were somehow destroyed by this bombardment,” he said. “The bombardment alone would not have done sufficient damage to have caused the comprehensive loss of primordial rocks on Earth, but if that bombardment also triggered additional eruptions, that could have buried the primordial rocks and plowed them back into the mantle.”

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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